Oregon State Vet Offers Seasonal Advice to Horse Owners

Oregon State Veterinarian Brad LeaMaster, DVM, PhD, advised owners to protect their horses against two viral threats by vaccinating against West Nile virus (WNV) and taking steps to prevent equine herpesvirus-1 (EHV-1).

Photo: Anne M. Eberhardt/The Horse

The season approaches for mosquitoes as well as horse shows and events. Oregon State Veterinarian, Brad LeaMaster, DVM, PhD, of the Oregon Department of Agriculture, advised owners on May 21 to protect their horses against two viral threats by vaccinating against West Nile virus (WNV) and taking steps to prevent equine herpesvirus-1 (EHV-1).

“It’s important for horse owners to vaccinate animals for West Nile Virus before the mosquito season kicks into high gear,” says LeaMaster. “The vaccine provides good protection and is available through local veterinarians.”

Infected wild birds are the source of WNV. Mosquitoes bite infected birds and then can potentially transmit the infection to horses and humans. The disease does not transmit from horse to horse or human to human. A bite by an infected mosquito is the only known route of transmission. A low percentage of mosquitoes carry the virus and a low percentage of horses bitten by infected mosquitoes become ill. But a horse showing signs is a serious situation. The disease causes brain inflammation and about one-third of affected horses die. Clinical signs include stumbling, lack of coordination, weakness in the legs, depression, muscle twitching, and death.

Insect control on individual animals also provides a good preventative measure along with reducing mosquito breeding sites. Any source of stagnant water can breed mosquitoes.

EHV-1 outbreaks have been reported in other states this spring, including California, but not yet in Oregon. EHV-1 is not transmissible to people, but it is a serious disease of horses that can cause respiratory, neurologic disease, and death. The virus is highly contagious. The most common way for EHV-1 to spread is by direct horse-to-horse contact. The virus can also spread through the air, or via contaminated equipment, clothing, and hands. Clinical signs include fever, decreased coordination, nasal discharge, urine dribbling, loss of tail tone, hind limb weakness, lethargy, and the inability to rise. While there is no cure, the veterinarians can treat some clinical signs.

“The EHV disease is very complex,” says LeaMaster. “Horse owners are advised to consult with their local veterinarian regarding vaccination and other preventative practices. They should continue to be vigilant by using strict biosecurity measures and hygiene practices. With a lot of horse shows and competitions scheduled over the next couple of months, owners should be aware of any outbreaks that might be taking place in other states where they are traveling.”

Horse owners are encouraged to contact their veterinarian with any questions about WNV or EHV-1.

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